1. Field of the Invention
The present invention relates to computers and computer cursor control input devices. More particularly, the present invention relates to a capacitive touch pad suitable for accepting input from a non-conductive stylus.
2. The Prior Art
Capacitive touch sensing devices (touchpads) are currently known in the art and are available from several manufacturers. The principle advantage of capacitive touch technology is sensitivity to fingers. Only very light contact is required to accurately detect the position of a finger on the pad. This feature makes capacitive touch sensors especially suitable as computer pointing devices.
Capacitive sensors have, so far, been limited to detecting conductive objects which create a large area of contact on the pad and have sufficient capacitance to be detected (for example, human fingers). Objects which are either small or not conductive are difficult to detect capacitively because they have very little capacitance. Thus, a plastic stylus or pen cannot be reliably and accurately detected by existing capacitive sensors. This limitation has excluded capacitive touch sensors from applications, such as graphics tablets, which may require pen input.
Resistive touch sensing devices are also well-known in the art, and substantially preceded capacitive touchpads in the market. Most resistive sensing devices require substantial pressure on the surface in order to accurately determine the point of contact. A stylus, which produces a small region of high contact pressure, is easily detected by resistive sensors. A light finger touch is difficult to detect using resistive technology, since the touch force is distributed over a larger area and there is no region of high contact pressure. Resistive technology has been adopted for applications which allow for greater contact force or do not require much positioning accuracy (e.g. touch screens).
While resistive touch sensing technology has existed for decades, it has never been widely adopted for computer pointing devices. Not until the light touch sensitivity made possible by the recent introduction of capacitive sensors have users accepted touchpads as a preferred input device in computer applications.
It is an object of the present invention to provide a capacitive touchpad which overcomes some of the limitations of the prior art.
It is an object of the present invention to provide a capacitive touchpad which can accept input from a non-conductive stylus.
It is a further object of the present invention to provide a capacitive touchpad which can accept input from a non-conductive stylus or a light finger touch.